Mine started bothering me when I felt a soreness on my tailbone and looked to see what appeared to be a pimple, but the sucker wouldn't go away!
It got to the severly-itching point, but I didn't scratch it, to my recollection, nor did I try taking any tool and rupturing it, althoughI tried 'assuming' a position that involved lying on my side with the INTENT of doing something about it! heh heh
Mine never drained or anything like that, although I think I had sweat 'issues' in the area when I was around 16. Maybe that was a clue that something was happening, but I had NO idea why the area would itch, and then I would scratch it, causing it to bleed.
Good luck!
I don't know if an ultrasound can give any insight regarding a pilonidal cyst. You can do a Search on here to find any relevant words...